Although it is considered that cancer cells always incidentally appear in a living body, it is hypothesized that the reaction by natural immunity normally occurs for elimination of a specific cancer antigen derived from cancer cells and that then a specific immune response is induced to cause the reaction of elimination of cancer cells by lymphocytes and other cells.
The recognition of a cancer cell-derived antigen requires the formation of a complex by a human leukocyte antigen (HLA) present on the cell surface and a lymphocyte. The HLA molecule as a major histocompatibility antigen is roughly divided into class I molecules (HLA types A, B, and C) and class II molecules (HLA types DP, DQ, and DR). The reaction of elimination of a cancer cell by a cytotoxic T cell (CTL) is induced by the specific recognition of a cancer antigen (CTL epitope) consisting of 8 to 11 amino acids which is presented on an HLA class I molecule on the cancer cell surface by a T cell antigen receptor (TCR) on the CTL.
The search for immunogenic peptides has been currently carried out with a view to their application to the treatment or prevention of various immune-related diseases; for example, Japanese Patent Laid-Open No. 08-151396 discloses that an oligopeptide consisting of a particular amino acid sequence has a HLA-binding capacity.